Electro-mechanical spatial light modulators have been designed for a variety of applications, including image processing, display, optical computing and printing. Optical beam processing for printing with deformable mirrors has been described by L. J. Hornbeck; see U.S. Pat. No. 4,596,992, issued Jun. 24, 1986, entitled "Linear Spatial Light Modulator and Printer". A device for optical beam modulation using cantilever mechanical beams has also been disclosed; see U.S. Pat. No. 4,492,435, issued Jan. 8, 1995 to Banton et al., entitled "Multiple Array Full Width Electro-mechanical Modulator," and U.S. Pat. No. 5,661,593, issued Aug. 26, 1997, to C. D. Engle entitled "Linear Electrostatic Modulator". Other applications of electro-mechanical gratings include wavelength division multiplexing and spectrometers; see U.S. Pat. No. 5,757,536, issued May 26, 1998, to Ricco et al., entitled "Electrically-Programmable Diffraction Grating".
Electro-mechanical gratings are well known in the patent literature; see U.S. Pat. No. 4,011,009, issued Mar. 8, 1977 to Lama et al., entitled "Reflection Diffraction Grating Having a Controllable Blaze Angle", and U.S. Pat. No. 5,115,344, issued May 19, 1992 to J. E. Jaskie, entitled "Tunable Diffraction Grating". More recently, Bloom et al. described an apparatus and method of fabrication for a device for optical beam modulation, known to one skilled in the art as a grating-light valve (GLV); see U.S. Pat. No. 5,311,360, issued May 10, 1994, entitled "Method and Apparatus for Modulating a Light Beam". This device was later described by Bloom et al. with changes in the structure that included: 1) patterned raised areas beneath the ribbons to minimize contact area to obviate stiction between the ribbon and substrate; 2) an alternative device design in which the spacing between ribbons was decreased and alternate ribbons were actuated to produce good contrast; 3) solid supports to fix alternate ribbons; and 4) an alternative device design that produced a blazed grating by rotation of suspended surfaces; see U.S. Pat. No. 5,459,610, issued Oct. 17, 1995, to Bloom et al., entitled "Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction Between Grating Elements and Underlying Substrate," and U.S. Pat. No. 5,808,797, issued Sep. 15, 1998 to Bloom et al., entitled "Method and Apparatus for Modulating a Light Beam." Bloom et al. also presented a method for fabricating the device; see U.S. Pat. No. 5,677,783, issued Oct. 14, 1997, entitled "Method of Making a Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction Between Grating Elements and Underlying Substrate".
The GLV device can have reflective coatings added to the top surface of the ribbons to improve the diffraction efficiency and lifetime of the GLV device. Preferred methods of fabrication use silicon wafers as the substrate materials requiring the device to operate in reflection for the wavelengths of interest. An increase in reflectivity is important to reduce damage of the top surface of the ribbons and avoid mechanical effects that might be attributed to a significant increase in the temperature of the device due to light absorption.
For GLV devices, the position and height of the ribbons has been symmetric in design. One drawback to this design is an inability to isolate the optical intensity into a single optical beam. This relatively poor optical efficiency is primarily due to the symmetry of the actuated device, which produces pairs of equal intensity optical beams. Each period of the improved grating must include more than two ribbons and create an asymmetric pattern of the ribbon heights. By creating an asymmetric pattern for the heights of the actuated ribbons, the intensity distribution of the diffracted optical beams is asymmetric and can produce a primary beam with a higher optical intensity. The direction of this primary diffracted beam can be switched by creating a different second actuated state for the ribbon heights. Unique to this work is the use of multiple heights in a GLV to create an asymmetric grating profile for improved optical diffraction efficiency that can be switched between two actuated states.